1. Field of the Disclosure
The present disclosure relates to an electric motor, and particularly, to an electric motor capable of preventing the occurrence of a short-circuit of a rotor.
2. Background
As is well known, an electric motor is commonly a rotary electric machine for converting electric energy into mechanical energy.
FIG. 1 is a sectional view of an electric motor in accordance with the conventional art, and FIG. 2 is a sectional view of a rotor of FIG. 1.
As shown in FIG. 1, the electric motor includes a stator 20, and a rotor 30 rotatably disposed with respect to stator 20. A frame or a case 10 is provided outside stator 20. A bearing 12 for rotatably supporting the rotor 30 is provided at the case 10. Stator 20 includes a stator core 22, and a stator coil 24 wound on stator core 22.
The rotor 30 includes a shaft 31, a rotor core 41 coupled to shaft 31, and a rotor coil 51 wound on rotor core 41. As shown in FIG. 2, rotor core 41 includes a hub 43 to which shaft 31 is coupled, and a plurality of poles 45 protruding from hub 43 in a radial direction. Poles 45 are spaced from each other at constant intervals in a circumferential direction. Slots 44 are formed between every two neighboring poles 45. Rotor coil 51 is wound on each pole 45 a plurality of times.
A power supply unit 35 for supplying power to rotor coil 51 is provided at shaft 31. Power supply unit 35 includes commutators or slip rings 36 coupled to shaft 31, and brushes 37 contacting the commutators or slip rings 36 to conduct power to rotor coil 51.
However, the conventional electric motor has the following problems. First, when rotor 30 rotates, coil ends or end turns of rotor coil 51 protruding from two ends of rotor core 41 in an axial direction are pulled in a radial direction. This may cause a short-circuit of rotor coil 51. Second, when the electric motor is driven, rotor coil 51 does not smoothly emit heat due to its relatively small contact area with the surrounding air. This may cause temperature increases of rotor coil 51. If rotor coil 51 has a drastic temperature increase, the electric motor may have a reduced output capability and perhaps permanent damage.